Fine Structure of Mistletoe Pollen. Iv. Eurasian and Australian Viscum L. (Viscaceae)

Abstract

Fifteen Eurasian and Australian species of Viscum L. were examined by light, scanning, and transmission electron microscopy. Pollen characters divide the species into two groups, each correlated with differences in habit and inflorescence structure: Group I (12 spp.) characterized by psilate or slightly sculptured exines and a non‐uniform ektexine pattern and Group II (3 spp.) possessing highly sculptured (echinate, rodlet) surfaces and uniform ektexine patterns. Within each of the groups, pollen characters divide the species into several subgroups. Among Group I, species V. nepalense, V. heyneanum and V. ovalifolium are particularly close. The Group I species, V. trilobatum, is placed in its own subgroup primarily because of its uniform ektexine pattern—a unique feature among Asian and Australian Viscum. Of the three Group II species, V. album and V. alniformosanae are palynologically almost indistinguishable. Pollen of the Group II V. cruciatum, though exomorphologically similar to V. album, is closest ultrastructurally to the Indian V. trilobatum. Overall, the most common and probably basic pollen characters among the Eurasian and Australian species include: subprolate, rounded convex almost spherical shapes; tricolporate apertures, and non‐uniform sculpturing and ektexine patterns. Oblate‐spheroidal or prolate‐spheroidal shapes, prominent sculpturing, and a uniform ektexine pattern are derived characters largely restricted to the Eurasian and Asian Group II species (V. album, V. alniformosanae, V. cruciatum).

Eocene Loranthaceae pollen pushes back divergence ages for major splits in the family

“…The outstanding work on the pollen morphology of extant Loranthaceae by Feuer & Kuijt (1979 , 1980 , 1985 ) and other Santalales lineages ( Maguire, Wurdack & Huang, 1974 ; Feuer, 1977 , 1978 , 1981 ; Feuer & Kuijt, 1978 , 1982 ; Feuer, Kuijt & Wiens, 1982 ) demonstrated that most pollen produced by members of the Loranthaceae cannot be confused with pollen from other angiosperm families ( Grímsson, Grimm & Zetter, 2017 ). Grímsson, Grimm & Zetter (2017) distinguished four general types (Pollen Type A, B, C, D), of which only one (Pollen Type A) could be confused with pollen of other Santalales lineages, and would unlikely be recognised as Loranthaceae pollen if found in a fossil pollen sample.…”